Infra red image tube



Dec. 19, 1961 G. A. MORTON 3, 4,

INFRA RED IMAGE TUBE Filed April 9, 1947 INVENTOR. 6502a: A. Monro/v BYWM 3,014,147 INFRA RED WAGE TUBE George A. Morton, Gait Ridge, Tenn, assignor to Radio Corporation of America, a corporation of Delaware Filed Apr. 9, 1947, Ser. No. 740,411 1 Claim. (Cl. 3I3-65) This invention relates to viewing tubes for observing objects in partial or total darkness and more especially to tubes for production of visible images from far infra red radiant energy.

Image tubes are of great importance in certain uses for observing objects in darkness. For this purpose there have been used imaging devices having phosphors that produce light from infra red energy when previously excited by blue or ultra violet light. In general, these devices are visually ineflicient because the light emitted is toward the red end of the spectrum.

Image devices have also been made with photocathodes that emit electrons when impinged by near infra red waves which electrons then cause a screen to fluoresce by bombardment thereof. This type of tube has along wave cutofi at about 11,000-l2,000 A. due to the inherent limitations of all known photoemitters and is not satisfactory for far infra red waves.

It is an object of this invention to provide an image device in which the photocathode is excited by light energy produced by a phosphor stimulated into luminescence by incident far infra red energy.

it is another object of the invention to provide an image device in which the color response of the phosphor upon which the far infra red energy impinges, is matched to that of the photocathode.

Another object of the invention is to reduce the magnification of the image to obtain increased brightness.

Other objects will appear in the following specification, reference being had to the drawing in which the single FIGURE of the drawing is a sectional elevation of a tube embodying the invention.

Referring to the drawing, the tube comprises an evacuated envelope 1 of suitable material, such as glass or metal, enclosing the elements for production of the light image. Anode cylinder 2 supports a glass disc 3 on the front side of which is a phosphor material 4 capable of eflicient production of light when stimulated by far infra red energy, say of 1 to 2 microns in Wave length for a time after excitation by blue or ultra violet light. The phosphor material 4 may, for example, be that disclosed in the application of Humboldt W. Leverenz, filed May 22, 1945, Serial No. 595,146, now Patent No. 2,527,365, which is strontium sulphoselenide with europium and samarium activators. The photocathode 5 on the other side of the glass disc may be a coating of caesiated silver.

Anode 6 is placed adjacent the latter and anode 7 is positioned adjacent anode 6. The anode 7 has a flange 8 with a reduced opening 9 adjacent to which is placed anode 10. The anode structure 7, 8, 9, 10 constitutes the main lens of de-magnifying electrostatic lens system, anodes 2 and 6 being Weak lenses. Cylinder anode 10 extends close to the end 11 of the envelope on which is coated the phosphor 12 capable of emitting light of high visual efiiciency by electron bombardment. Various phosphors may be used, for example, such as willemite, zinc sulphoselenide, and zinc cadmium sulphide with their known activators. The image on the phosphor 12 is reduced in size compared to that on the phosphor 4 and its brightness is correspondingly increased.

iii-ates Pater O Fatented Dec. 19, 1961 The anodes 2, 6, 7 and 10 will be of suitable dimensions and will have suitable positive voltages applied thereto relative to the photocathode, such as those given in my application filed April 5, 1947, Serial No. 739,717, but, of course, those skilled in the art will be able to vary these as desired.

A suitable lens system will, of course, be used to focus the infra red energy on the phosphor 4, and a suitable lens system will be used to magnify the reduced image produced on the phosphor 12. These are well known in the art and are not part of the claimed invention. They, therefore, are not shown in the drawing.

In the operation of the viewing tube, the phosphor 4 will be excited by a blue or ultra violet source not shown and when the excitation is removed the phosphorescence will decay to invisibility after a short period but when the far infra red energy radiated from an object in the dark is focused on the phosphor to produce an image thereon the phosphor will at once be stimulated to release energy stored by the blue or ultra violet light and a light image of the object in red or reddish light will be produced in phosphor 4. This is visually inefiicient but the red or reddish light will eificiently excite the photocathode 5 to emit electrons which are electrostatically focused on phosphor 12 to produce a luminescent image of reduced size giving increased intrinsic brightness.

It will be seen that I utilize the red light of the phosphor produced by the incident far infra red energy, to excite a photocathode, and using the photoelectrons emitted thereby to efiiciently excite the phosphor 12 which produces an image of high visual efliciency.

The photocathode 5 may be deposited on the inside of the front end of the envelope 1 and the phosphor 4 may be deposited on the outside of the tube end but unless the phosphor is protected from moisture and abrasion by a transparent varnish, it will not be so satisfactory an arrangement.

Instead of first exciting the phosphor 4 with blue or ultra violet light, I may use other radiation such, for example, as emanation from radio active materials.

Various other modifications may also be made without departing from the spirit of the invention.

What I claim as new is:

An image tube comprising an evacuated envelope containing a glass disc near one end, a phosphor on one side of said disc stimulatable to emit light by far infra red energy for a time after previous excitation by radiant energy of shorter wave lengths, a photocathode on the other side of said disc adapted to emit photoelectrons when excited by the light emitted by said phosphor, a second phosphor at the other end of said envelope of lesser size than the first-mentioned phosphor, and a series of cylindrical elongated anodes of successively decreasing diameter between said photocathode and said second phosphor for focusing said photoelectrons thereon to produce an image of less size than the light image on the first-mentioned phosphor.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,226 Kunz et al Mar. 16, 1937 2,177,360 Bussc Oct. 24, 1939 2,189,321 Morton Feb. 6, 1940 2,198,479 Langmuir Apr. 23, 1940 2,225,044 George Dec. 17, 1940 

